A pump or laser combiner is one of important components in a high power optical fiber laser system, and the pump is used to be a laser diode pump and the laser combiner provides optical fiber laser to inject into the high power optical fiber laser system. Referring to a power source for driving system, because a laser combiner can be coupled to multiple mode optical fibers that have a higher luminance, the power in multiple bundles can directly be coupled to be a high power multiple mode optical fiber laser by the laser combiner. However, with a coupling power increasing, a laser combiner often has a problem with overheating caused by the residual power on the cladding thereof, and it may limit the coupling power of the laser combiner.
In the prior art, there are some discussion about an optical fiber having thermally protecting structure. For example, disclosed in U.S. 2015/0049983 A1 is an optical fiber device that has a mode stripper thermally protecting structural adhesive composition. As disclosed in the patent, an output fiber of the optical fiber device has a first layer of mode stripper adhesive and a second layer of structural adhesive, and the mode stripper adhesive is positioned closer to the first optical element than the structural adhesive to strip a majority of power of cladding guided mode so that the power fails to reach the structural adhesive. The mode stripper adhesive has a lower hardness as compared to the structural adhesive, and is refractive indexed matched to an outermost layer of the output fiber that it is in direct contact with. However, disclosed in the patent, the mode stripper consists of a composition that has a refractive index higher than a refractive index of the surface of the cladding, and the composition can be heated by power of the light stripped so that a maximum stripping power is substantially limited and the operative power of optical fiber device is also limited.
U.S. 2014/0241385 A1 discloses a low-mode high power fiber combiner that is configured with a combiner end fiber spliced to a combiner output fiber. A light stripper is provided on specific zones along the combiner end fiber and output fiber and the specific zones are provided with respective refractive indices and materials, and may respectively strip laser light caused by forward and back-reflected light to protect the combiner for operating properly. Disclosed in the patent, there are various way to strip forward and back-reflected laser light power so that the stripped power may be converted into heat to disperse to different zones of the optical fiber, and thus the tolerant power of the combiner can be raised. However, the configuration may increase the total length of the combiner and the complexity of system.
U.S. Pat. No. 7,532,792 B2 discloses an optical coupler, a method of its fabrication and use, wherein the optical coupler consists of at least two input fibers and one output fiber. The input fibers are bundled into a bundle and extended to a taper to reduce a cross sectional area of the bundling structure, and an end of the input fiber may engage to an input face of the output fiber. Described in the patent, a power optical coupler can be made by a soluble silicate, such as for example sodium silicate and serves as a cladding power stripper to remove the laser light power propagating in the cladding. Also described in the patent, sodium silicate coated on a surface of the optical fiber is 2 mm in length, the drying for the surface coated with sodium silicate is performed using force air after finishing the coating, and small flakes of sodium silicate are formed on the surface. The coating material is attached to the cladding of the optical fiber to leave a non-smooth surface of the cladding for scattering the light power of the cladding. In addition, sodium silicate is heated such that the layer of sodium silicate inside may produce bubbles, and the bubbled surface improves the scattering performance of the light power. However, the soluble silicate used in the patent has a higher melting point, and must be optical use level to meet the requirement of a high power application. Also, the process of drying or heating may affect a stripping rate of the cladding power, even has a risk to damage the structure of device.
Therefore, a need exists in the industry for developing an optical fiber laser combiner that has a higher tolerant power, and is easy to integrate with a process of laser combiner without increasing the volume of the device. The tolerant power and bundling power of the optical fiber laser combiner can be raised to increase the output power of the optical laser.